Tone generator for electronic musical instrument

ABSTRACT

In an electronic musical instrument, a tone generator consists of two sections. A first section comprises a single master oscillator and a plurality of frequency dividers having respective frequency dividing ratios for dividing the master oscillator frequency to obtain some of twelve notes in an octave. A second section comprises a frequency shifter for shifting a frequency from the first section and frequency dividers for dividing the shifted frequency to obtain the rest of notes in the octave.

United States Patent 11 1 Nakada 1111 3,840,689 14 1 Oct. 8, 1974 TONE GENERATOR FOR ELECTRONIC MUSICAL INSTRUMENT [30] 1 Foreign Application Priority Data 3,601,518 8/1971 Hill 84/101 3,617,901 11/1971 Franssen 84/D1G. 11 3,639,853 2/1972 Sakai 1. 84/].01 X 3,735,013 5/1973 Van der Peet et a1... 1. 84/125 3,740,450 6/1973 Deutsch .1 84/1124 3,743,756 7/1973 Franssen et a1 1. 84/101 3,795,754 3/1974 Mochida 84/101 FOREIGN PATENTS OR APPLICATIONS 496,068 9/1950 Belgium 84/101 Primary Examiner-Stephen J. 'Tomsky Assistant ExaminerStanley J1 Witkowski 1221131 133 125223:112:11:iif'iiijijiif" 3233321; Attorney, Agent, or Firm-Holman & Sen

[52] U.S. Cl 84/l.0l, 84/124, 84/DIG. 11 [57] ABSTRACT [51] Int. Cl. ..G10h 5/06 I 1 t t [58] Field of Search 84/10], 1.03, DIG. 1 l, 523 :3853: 2332 25, fi gfi gego3125123325 D10 5 single master oscillator and a plurality of frequency dividers having respective frequency dividing ratios [56] UNITE r S :ZqrENTS for divitditng {the master oscillator frequency 30 obtain some 0 we ve notes 1n an octave. secon sectlon 3,215,767 11/1965 Martin 84/124 ompri s a frequency shifter for shifting a frequency 3,479,440 11/1969 Martin et a1. 84/ 1.25 from the first section and frequency dividers for divid- 327 l/1970 Volpe 84/ 1.01 ing the shifted frequency to obtain the rest of notes in 3,499,090 3/1970 Meyer 84/1.01 the Octave, 3,509,454 4/1970 Gossel 84/101 X 3,590,131 6/1971 Reyers 84/103 5 Claims, 5 Drawing Figures FREQUENCY DIVIDER D11 I I Ga f-Af o D FREQUENCY F8 55%;? SHIFTER l o E n5 M f i EF 2 EQuENcY B DIVIDER 1 --O C MASTER o F OSCILLATOR 11:9 Dlg C V g 1 FREQUENCY l DIVIDER c D22 FREQUENCY DIVIDER PATENIEUBCI 81274 SHEEI 3 OF 4 FIG.

F DC2 FREQUENCY DIVIDER DETECTER i m l MASTER OSCILLATOR FREQUENCY D I V I D ER TONE GENERATORFOR ELECTRONIC MUSICAL INSTRUMENT BACKGROUND OF THE INVENTION DESCRIPTION OF PRIOR ART According to one of the tone generator systems in an electronic musical instrument, musical scale tones have been generated by a tone generator as shown in FIG. 1. That is, the required musical scale tones C, B have been obtained by dividing an oscillating frequency of a single master oscillator M by means of frequency dividers Db, D DB, respectively. Accordingly, in order to reduce the pitch errors of notes in a musical scale consisting of 12 notes per octave, it is necessary to increase the oscillating frequency of the master oscillator M and also the number of the frequency-divider stages. On the other harid, if the number of the frequency-divider stages were decreased with the oscillating frequency of the master oscillator lowered, the pitch errors of the musical scale tones would inevitably increase.

SUMMARY OF THE INVENTION Accordingly, a first object of the invention is to provide a new tone generator of an electronic musical instrument in which the pitch errors of musical scale tones are decreased.

A second object of the present invention is to provide a tone generator of an electronic musical instrument in which musical scale tones of high accuracy are obwhen read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a block diagram'illustrating a conventional tone generator of an electronic musical instrument;

FIG. 2 is a block diagram showing one embodiment of the present invention;

FIG. 3 is also a block diagram illustrating a more specific example of the circuit composition shown in FIG.

tained by the user of a master'oscillator whose oscillating frequency is relatively low.

A third object of the present invention is to provide a tone generator of an electronic musical instrument in which musical scale tones which are highly accurate in pitch are generated by obtaining a beatfrequency signal caused between two different signals in addition to frequency division in the process of dividing an output frequency of a master oscillator. A fourth object of the present invention is to provide a tone generator of an electronic musical instrument in which those musical scale tones whose pitch errors would be large if only a frequency-division method were utilized are now generated on the basis of a signal produced from a frequency shifter thereby to considerably reduce the pitch errors.

A fifth object of the present invention is to provide a tone generator of an electronic musical instrument which is suitable for being produced as an integrated circuit.

According to the present invention, briefly summarized there is provided a tone generator in an electronic musical instrument, which employs a frequencydivision type tone generator system, and more particularly to atone generator which employs a master oscillator which oscillates a frequency not very high, thereby to obtain musical scale tones with high accuracy at a small number of frequency-dividing stages.

The foregoing objects and other objects of the present invention will become more apparent from the following, detailed description and the appended claims FIG. 4 is a block diagram showing another embodiment of the present invention; and

FIG. 5 is also a block diagram illustrating a more specific example of the circuit composition shown by the block diagram of FIG. 4.

DETAILED DESCRIPTION OF THE-INVENTION With reference now to FIG. 2, there is shown an embodiment of the present invention, in which the tone generator comprises: a master oscillator M; a frequency shifter FS which is adapted to shift high or low an output frequency (f) of the master oscillator M by a desired frequency (Af) by single side-band SSB) modulation or the like; frequency dividers D through D with frequency-dividing ratios N,N create several of musical scale tones by dividing the output frequency of the frequency shifter FS: and frequency dividers D through D with frequency-dividing ratios N N, create the rest of musical scale tones by dividing the output frequency of the master oscillator M. i

The musical scale tones can be classified into two groups namely, a first group which includes the musical scale tones whose pitch errors are not so large even by divisions of the frequency (f) of the master oscillator M, and a second group which includes the musical scale tones whose pitch errors can be small only by di visions of the frequency (f- Af) or (f+ Af) of the frequency shifter FS. As is apparent from FIG. 2, the first group ofmusical scale tones E, B, A, C# F, C, D and F# are produced by dividing the output frequency of the master oscillator M, and the second group of musical scale tones G# A# G and D# are produced by dividing the output frequency of the frequency shifter FS whose output frequency is (f Af). However, it is preferable that such distribution of the musicalscale tones be achieved by judging from the whole arrangement of the tone generator.

In this circuit, when a signal having the frequency (f) is produced from the master oscillator M, the signal is fed, as it is, to the frequency dividers D through D At the same time, the signal is fed to the frequency shifter FS where the frequency of said signal is shifted high or low by the frequency Af, and the thus shifted frequency is supplied to the frequency dividers D through D,,. The frequency dividers D through D divide the output frequency (f) of the master oscillator M in accordance with their predetermined frequencydividing ratios thereby to produce signals whose frequencies correspond to the musical scale tones E, B, A F# respectively. The specific internal construction of the various frequency dividers forms no part of the instant invention which, as aforestated, is directed to the disclosed novel combination and interconnection of frequency divider units with the master oscillator M and frequency shifter Fs. Any well-known and conventional frequency divider can be used, the dividing ratio of which can be selected as required in conventional fashion. Some of such conventional frequency divider constructions can be found in a publication entitled Functional Circuits and Oscillators by Herbert J. Reich, D. Van Nostrand Co., Inc., 1961, page 163, paragraph 37.5, and in the book entitled Pulse and Digital Circuits by Jacob Millman and Herbert Taub, published in 1956 by the McGraw-Hill Book Co. of New York, for example, chapter 11, paragraphs 11.3 and 11.4 and chapter 17, paragraph 17.6.

The frequency shifter FS is formed, for instance, on the basis of single sideband modulation, and, therefore, an output signal of the frequency shifter FS has a frequency which is obtained by shifting its input signal by a predetermined frequency. A signal having a frequency which corresponds to the frequency-shifting quantity described above, i.e. Af, may be obtained from a frequency-dividing circuit which is used for producing the musical scale tones or from a separate frequency divider.

The output of the frequency shifter FS is applied to the frequency dividers D through D and the frequency of the thus applied output is divided by the frequency dividers D through D,., in accordance with their frequency-dividing ratios, respectively, thereby to create signals which have frequencies corresponding to the musical scale tones G# A# G and D# respectively.

As an example, the values in FIG. 2 are selected as Referring now to FIG. 3, there is shown a preferred embodiment of the present invention which is illustrated more specifically than in FIG. 2. For convenience in description, the distribution of the musical scale tones in FIG. 3 is made the same as that in FIG. 2. In this embodiment, the frequency of a master oscillator M is determined by the frequencies of musical scale tones which are assigned to this tone generator and also by the composition of frequency dividers arranged in this example. In this case, the frequency of the master oscillator M is 419.013 kHz. The output frequency (f-Aj) of the frequency shifting circuit FS is preferably 396.062 kHz, judging from the tolerable values for the pitch errors of the assigned musical scale tones. Therefore frequency-shifting quantity (Af) of the frequency shifter FS is 22.051 kHz which is l/ 19.002 of the frequency of the master oscillator M.

In this connection, a frequency divider D whose frequency dividing ratio is His provided. The frequency divider D produces the frequency-shifting frequency (Af), and the thus produced frequency (Af) is fed to the frequency shifter FS. As a result, the output frequency of the frequency shifter FS will be 396.962 kHz.

The output frequency of the master oscillator M, that is, the signal of 419.013 kI-Iz, is applied to a first group of frequency dividers D. through D D through D D and D and is divided by these frequency dividers. As a result, signals corresponding to the musical scale tones E, B, A, C# F, C, D and F# are produced therefrom.

The output frequency of the frequency shifter FS, that is, the signal of 396.962 kHz, is supplied to a second group of frequency dividers D D D D and D and is divided by these frequency dividers. As a result, signals corresponding to the musical scale tones G# A# G and D# are produced therefrom.

The ratio of the oscillating frequency (f) of the master oscillator to the shifting frequency (Aj) of the frequency shifter FS is maintained constant by means of the frequency divider D Therefore, the relationships between the musical scale tones in FIG. 3 are constant throughout one octave. The shifting frequency (Af) to be fed to the frequency shifter FS can be optionally selected. The pitch error of the tone A# would be O.l29 percent according to conventionalsystem as shown in FIG. 2, but is is improved to 0.053 percent in the embodiment shown in FIG. 3.

As stated in the above description, the signal which is obtained by shifting the frequency (f) of the master oscillator M by the predetermined frequency (Af) is produced in the embodiment of the present invention shown in FIG. 3. However, the frequency-shifting operation may be carried out after the frequency-dividing operation. In addition, the frequency-dividing ratios of the frequency dividers D through D may be reduced to have as many prime numbers (factors) as possible, and if there are found any prime numbers which are in common as frequency-dividing ratios, a common frequency-dividing circuit may be established for these common prime numbers.

With reference now to FIG. 4, there is disclosed another embodiment of the present invention, which, similarly to the example in FIG. 2, comprises a master osicllator M which serves to oscillate a frequency (f), frequency dividers D and Dpg which produce the mu-' sical scale tone F, frequency dividers D and D which produce the musical scale tone C, a beat frequency oscillator BFD as a frequency shifter which shifts the frequency of the output of the frequency divider D used for the musical scale tone F by a frequency of the output of the frequency divider D used for the musical scale tone C, thereby to produce a difference frequency signal between these two outputs, and a frequency divider D which produces the musical scale tone D from the output of the beat frequency detector BFD.

In order to produce signals corresponding to the musical scale tones F and C, the oscillating frequency (f) of the master oscillator M is divided by the frequency dividers into desired frequencies. In other words, for the musical scale tone F the oscillating frequency (f) of the master oscillator M is divided by the frequency divider D at its frequency-dividing ratio of l/n,, and then the thus divided frequency is further divided by the frequency divider D at its frequency-dividing ratio of l/n as a result of which a signal F having a frequency f/(nym) is obtained.

For the musical scale tone C, the frequency (f) of the master oscillator M is divided by the frequency divider D at its frequency-dividing ratio llm and the thus divided frequency is further divided by the frequency divider D at its frequency-dividing ratio llm as a result of which a signal C having a frequency f/(m -m is produced. The output (f/m) of the frequency divider D and the output (flm of the frequency divider D are fed to the beat frequency detector BFD which may be; for instance, a heterodyne detector. The beat frequency detector BFD produces a difference frequency signal (f/n f/m between the two signals (f/n and flm and this difference frequency signal is fed to the frequency signal divider D The frequency divider D in turn divides the thus fed signal at its frequency-dividing ratio 1/l thereby to produce the musical scale tone D having a frequency (f/n f/m )-1/l.

It is necessary in the selection of the abovementioned two signals that a difference between the frequenciesof the twosignals be equal to or very close to an integer multiple of the frequency of a tone pitch to be produced. That is, the two signals cannot be randomly selected. Therefore, the tone generator circuit must be organized by properly selecting the frequencydividing ratios of the frequency-dividing circuits and by suitably providing signal pickup points in the tone generator circuit.

With reference to FIG. 5, an embodiment of the present invention which more specifically embodies the block diagram of FIG. 4 will now be described. In this example, the musical scale tones D and A are produced on the basis of a difference frequency signal between frequency divider stages used for the musical scale tones F and C.

It will be assumed that the oscillating frequency of the master oscillator is 444.393 kHz, the first stage D of the frequency-dividing circuit for the musical scale tone F has a frequency-dividing ratio l/ 3, and the first stage D and D of the frequency-dividing circuit for the musical scale tone C has a frequency-dividing ratio 1/25 (or 1/5 X US). Two signals which pass respectively through these first stages are applied to a beat frequency detector BFD. Since the two inputs of the beat frequency detector. BFD are originally supplied from the master oscillator M, they are the same in phase and amplitude but different in frequency. Therefore, a signal detected by the detector BFD is exactly in correspondence to the output signal of the master oscillator M. The detected signal frequency is divided by a frequency divider D at a frequency-dividing ratio- H37 and is further divided by a frequency divider D at a frequency-dividing ratio 1/3 thereby to produce the musical scale tone D. Furthermore, the detected signal frequency which has been divided by the frequency divider D is divided by a frequency divider D at a frequency-dividing ratio V2 thereby to produce the musical scale tone A.

The thus produced musical scale tone D has a frequency of 1174.4 Hz, which deviates only 0.024 percent from its nominal frequency 1174.7 I-Iz, while the thus produced musical scale tone A has a frequency of 17616 Hz, which deviates only 0.088 percent from its nominal frequency 1760.0 Hz.

In the conventional tonegenerator, the musical sound tones D and A are produced by dividing the output frequency of, for instance, the frequency divider D at ratios-of l/3 l/3 H3 and H3 l/3 X A, respectively. The thus produced musical tone D deviates 0.079 percent from its standard frequency, while the corresponding error of the tone A is 0.200 percent.

As is apparent from the above descriptions, both the musical scale tones D and A produced in accordance with the present inventionare less than half in error and much improved inaccuracy when compared with those produced onlyby the conventional tone generator including the frequency division system as shown in FIG. 1. In the case of the musical scale tone production by the conventional frequency division system only, the musical scale tone A has the maximum positive error, but according to the present invention the musical scale tone G, improved as described above, has the maximum error. The tone which has the maximum negative error is G# in the conventional circuit and also in the present invention.

I claim:

1. YA method for generating notes having reduced pitch errors in an electronic musical instrument, the method comprising the steps of:

frequency-dividing a preselected frequency to produce a plurality of preselected notes from an octave;

' frequency-shifting said preselected frequency by a predetermined modulating frequency to obtain a frequency shifted signal;

frequency-dividing said frequency shifted signal to obtain remaining notes of said octave other than said preselected notes, to thereby reduce pitch errors in said remaining notes.

2. A tone generator for an electronic musical instrument, comprising: a single master oscillator and a first musical tone generator-series connected thereto and including frequency-dividing means for directly frequency-dividing a frequency produced by the master oscillator to produce frequencies for certain notes of an octave; frequency-shifting means for shifting the frequency of the master oscillator by a predetermined modulating frequency, said frequency shifting means being connected to the master oscillator and delivering a frequency-shifted tone signal; at least a second tone generator-series connected to said frequency-shifted tone signal and including a second set of frequencydividing means to produce frequencies of the remaining notes other than said certain notes, whereby, because of frequency division of said frequency-shifted tone signal, pitch-errors of said remaining notes are limited to be within predetermined tolerences.

3. A tone generator as in claim 2, which includes means for maintaining a ratio of the frequency of the master oscillator to the modulating frequency constant.

4. A tone generator for an electronic material instrument, comprising:

a single master oscillator and a first musical tone ering a frequency-shifted tone signal, said frequency-shifting means comprising a beat-frequency de- 7 .8 tector connected between outputs of said first and certain notes, whereby, because of frequency divisecond frequency divider so as to obtain the fresion of said frequency-shifted tone signal, pitchquency-shifted tone signal; and errors of said remaining notes are limited to be at least a second tone generator-series connected to within predetermined tolerances.

said frequency-shifted tone signal and including a 5. A tone generator as in claim 4 wherein said beatsecond set of frequency-dividing means to produce frequency detector comprises a heterodyne detector. frequencies of the remaining notes' other than said 

1. A method for generating notes having reduced pitch errors in an electronic musical instrument, the method comprising the steps of: frequency-dividing a preselected frequency to produce a plurality of preselected notes from an octave; frequency-shifting said preselected frequency by a predetermined modulating frequency to obtain a frequency shifted signal; frequency-dividing said frequency shifted signal to obtain remaining notes of said octave other than said preselected notes, to thereby reduce pitch errors in said remaining notes.
 2. A tone generator for an electronic musical instrument, comprising: a single master oscillator and a first musical tone generator-series connected thereto and including frequency-dividing means for directly frequency-dividing a frequency produced by the master oscillator to produce frequencies for certain notes of an octave; frequency-shifting means for shifting the frequency of the master oscillator by a predetermined modulating frequency, said frequency shifting means being connected to the master oscillator and delivering a frequency-shifted tone signal; at least a second tone generator-series connected to said frequency-shifted tone signal and including a second set of frequency-dividing means to produce frequencies of the remaining notes other than said certain notes, whereby, because of frequency division of said frequency-shifted tone signal, pitch-errors of said remaining notes are limited to be within predetermined tolerences.
 3. A tone generator as in claim 2, which includes means for maintaining a ratio of the frequency of the master oscillator to the modulating frequency constant.
 4. A tone generator for an electronic material instrument, comprising: a single master oscillator and a first musical tone generator-series connected thereto and including frequency-dividing means for directly frequency-dividing a frequency produced by the master oscillator to produce frequencies for certain notes of an octave, said frequency-dividing means of said first musical tone generator-series comprising at least first and second frequency dividers of known dividing ratios; frequency-shifting means for shifting the frequency of the master oscillator by a pre-determined modulating frequency said frequency-shifting means being connected to the master oscillator and delivering a frequency-shifted tone signal, said frequency-shifting means comprising a beat-frequency detector connected between outputs of said first and second frequency divider so as to obtain the frequency-shifted tone signal; and at least a second tone generator-series connected to said frequency-shifted tone signal and including a second set of frequency-dividing means to produce frequencies of the remaining notes other than said certain notes, whereby, because of frequency division of said frequency-shifted tone signal, pitch-errors of said remaining notes are limited to be within predetermined tolerances.
 5. A tone generator as in claim 4 wherein said beat-frequency detector comprises a heterodyne detector. 